1. Field of the Invention
This application relates generally to networking devices, and, specifically, to methods for configuring such devices so that they provide virtual router functionality, i.e., present different virtual router configurations to different end users, classes of service or packets.
2. Related Art
Virtual router functionality refers to the capability of the same physical networking device to present different virtual router configurations to different end users, classes of desired service, or packets. As a result of this capability, the same physical device appears as a plurality of different virtual routers. To implement this capability, current routers directly map a packet field of interest, typically the VLAN field, into the identifier of a particular routing table, and then use the particular routing table to route the packet. The VLAN field designates a virtual LAN, a collection of network elements that may be physically disparate but are logically related such that they may be considered part of the same LAN for OSI layer two routing/switching purposes. For example, all the network elements in a particular VLAN receive broadcasts from any other element in the VLAN at OSI layer two.
This approach, whereby the VLAN of the incoming packet is directly mapped into an identifier of a routing table, worked fine as long as different end users used non-overlapping VLANs, so that the VLAN could be used to present different virtual routers to different end users. However, as VLAN usage proliferated, different end users began using overlapping sets of VLANs, so the VLAN could no longer be used to present different virtual routers to different end users.
Another problem is that the number of virtual routers that are possible is limited by the size of the VLAN field. A VLAN of 12 bits, for example, identifies only 4 K different routing tables, which may not be sufficient for certain applications.
A third problem is the lack of flexibility in this approach. If, for example, the VLAN type or format changes as network usage evolves or as network standards change, the approach would be rendered obsolete as it is tied to a particular VLAN type and format.
A fourth problem is the lack of scalability of this approach with an increase in the number of virtual routers that may need to be accommodated. With this approach, for example, an increase in the size of the VLAN field to allow for an increase in virtual routers multiplies in direct proportion the number of routing tables that need to be maintained.